1. Field of the Invention
2. Description of Related Art
The present invention relates to a method and a device for transferring at least two sheets, which are arranged in a shingled mode of arrangement in a sheet or paper transport direction, to a sheet or paper handling machine in which the at least two sheets are moved at a first speed after the transfer.
In the prior art, paper handling systems are known in which e.g. 2-up printed sheets are supplied to a cutter, separated from one another by this cutter and then placed ready for further processing by a subsequent device. For this purpose, the 2-up printed sheets are placed one on top of the other by means of suitable machines, such as mergers, and, in this condition, they are applied to subsequent paper handling machines for further processing.
For further processing the individual sheets provided in this way, the subsequent machines take over, per machine clock cycle, one such waiting sheet; depending on the subsequent machines, individual groups must e.g. be formed from the sheets provided, these groups being then e.g. put in envelopes.
The clock cycle with which the cutter operates and with which the individual sheets are made available to the subsequent machines is faster than the clock cycle of a subsequent enveloping unit. By way of example, it is assumed that the cutter can carry out 1,000 cutting operations within a predetermined period of time, whereas the enveloping unit can carry out 100 enveloping operations within this period of time. This has the effect that, in a first case, in which the enveloping unit processes only single sheets, the cutter will be stopped at certain intervals, since it would provide too many sheets, whereas in a second case, in which the enveloping unit envelops fifteen sheets at a time, the enveloping unit will have to be stopped at certain intervals, since the cutter is not able to provide a sufficient number of sheets. The prior art already discloses solutions which, for avoiding the disadvantages resulting from the above, interpose a buffer between the cutter and the subsequent machines so as to permit a continuous operation of the cutter. In this case, the individual sheets discharged by the cutter are introduced in the buffer, and, when a predetermined number of sheets has been reached, switching over to e.g. a second buffer plane is effected so that the sheets contained in the first buffer plane can be advanced for further processing, whereas sheets discharged by the cutter are simultaneously introduced in the second buffer. Such a device is described e.g. in U.S. Pat. No. 5,083,769.
Devices of this type are, however, disadvantageous insofar as the transfer of the sheets which are discharged by the cutters and which have been merged by the merger takes too much time, since the individual sheets must be transferred to the buffer one after the other. When the sheets are provided in pairs, two sheets at a time can be transferred in parallel. In the case of large groups two sheets at a time are transferred in parallel, the respective pairs of sheets being transferred in succession. Furthermore, the performance will be impaired in the case of comparatively large buffers or uneven numbers of sheets or group sizes or in the case of even numbers of sheets and a discharge which does not take place in pairs, since, for forming a group, such systems need two or more clock cycles depending on the number of sheets.
Starting from this prior art, it is the object of the present invention to provide a method and a device which support a simple and a faster formation of groups with a minimum number of necessary machine clock cycles in paper handling systems.
This object is achieved by a method according to claim 1 and a device according to claim 7.